How to change the "departure" of the popup?

Question

css

now - leaves with a black background ,

I want to achieve - a black background should appear
and everything that goes on top of it

moved the necessary styles to the very bottom (for convenience)
https://jsfiddle.net/ef3xbjhw/5/

Answer 1

Need to add to CSS:

.popup__menu--active{
    transition: background-color 1s ease;
}

It is better to change the time for example by 0.25s.
Also, an example on jsFiddle